An alarm according to a first conventional art detects heat, smoke, a gas, light of a flame, and the like caused by a fire, and determines that there is a fire from them individually, or from a combination thereof in order to prevent a false alarm or the like. A signal which is outputted on detection of a fire is sent to a fire extinguishing device and, along with a bell or the like being rung, a sprinkler or the like operates.
As an alarm according to a second conventional art, there is disclosed a fire alarm which can inform even people with a hearing impediment of the occurrence of a fire when a fire occurs. This fire alarm informs of the occurrence of an unusual situation, namely a fire by diffusing an odorant when a fire occurs. In this fire alarm, mainly methyl mercaptan is used as a gas odorant (for example, refer to Japanese Unexamined Patent Publication JP-A 2004-326326).